Rotor blade for a wind power plant

ABSTRACT

The present invention concerns a rotor blade for a wind power plant having an aerodynamic profile comprising a rotor blade leading edge and a rotor blade trailing edge. The invention also concerns a rotor blade tip for a rotor blade having an aerodynamic profile with a pressure and a suction side, wherein the rotor blade tip is curved or angled in its end region in the direction of the pressure side of the rotor blade. In order further to reduce the levels of sound emission of wind power plants the rotor blade is curved or angled in its edge region in the direction of the trailing edge of the rotor blade in the plane of the rotor blade. In that respect the invention is based on the realization that, in the case of a rotor blade which does not go to a point at the tip, the effective rotor blade area is maintained unreduced precisely in the outer region in which the effect is greatest. The curve or angling of the end region of the rotor blade however provides that the trailing edge is displaced rearwardly in the end region of the rotor blade so that the flow at the rotor blade trailing edge is detached with a time delay in the outer region. Alternatively to attain the object of the invention a rotor blade can be developed in such a way that the ‘outer region’ narrows. That configuration of the rotor blade tip is based on the realization that the decreasing blade depth results in a reduced flow around the blade tip as the energy thereof is previously distributed to the trailing edge vortices but at the same time the effective rotor blade area is also reduced. The angling of the rotor blade tip provides that the effective rotor blade depth remains at its optimum as far as the angled rotor blade tip.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a rotor blade for a wind power planthaving an aerodynamic profile comprising a rotor blade leading edge anda rotor blade trailing edge. The invention also concerns a rotor bladetip for a rotor blade having an aerodynamic profile with a pressure anda suction side, wherein the rotor blade tip is curved or angled in itsend region in the direction of the pressure side of the rotor blade.

2. Description of the Related Art

Such rotor blades and rotor blade tips have long been known in the stateof the art. In particular curved rotor blade tips have been used forsome time for example in rotor blades from the manufacturer Enercon.Those known rotor blade tips are intended to reduce the edge vorticeswhich inevitably occur at the rotor blade end, and thus reduce theoccurrence of unwanted noise.

As state of the art attention is directed at this juncture generally tothe following publications: DE 197 38 278; DE 197 43 694; DE 44 40 744;DE 196 14420 and DE 4436 197.

Rotor blades of the kind set forth in the opening part of thisspecification are also known, the tips of which terminate elliptically.That configuration of the rotor blade tips is also intended to reducethe levels of noise emission from the rotor blade and in particular thetip thereof.

As wind power plants are now no longer individual phenomena but are tobe encountered in many places, they are also increasingly to be found inthe proximity of residential areas. It is precisely there that theacceptance of wind power plants is dependent inter alia on the soundemission and it is readily appreciated that quieter wind power plantsare accepted more readily than loud ones.

BRIEF SUMMARY OF THE INVENTION

Therefore the object of the present invention is to further reduce thelevels of sound emission of wind power plants.

In a rotor blade for a wind power plant of the kind set forth in theopening part of this specification that object is attained in that therotor blade is curved or angled in its end region in the direction ofthe trailing edge of the rotor blade in the plane of the rotor blade. Inthat respect the invention is based on the realization that, in the caseof a rotor blade which does not go to a point at the tip, the effectiverotor blade area remains unreduced precisely in the outer region inwhich the effect is greatest. Curving or angling the end region of therotor blade however means that the trailing edge is displaced rearwardlyin the end region of the rotor blade so that the flow at the rotor bladetrailing edge is detached in the outer region with a time delay. Thatalso reduces the influence of the vortices which occur upon separationof the flow from the rotor blade trailing edge, with each other, andthus also the sound emission emanating therefrom. It is precisely in thecase of a windward rotor that the interaction between the flow aroundthe blade tip and the dynamic air pressure in front of the plant pylonis also reduced by the invention.

In that respect the time delay is dependent on the angle at which theend region extends in relation to the thread axis of the rotor blade.The greater the respective angle, the better is the degree of reductionin noise emission. As on the other hand however torsional moments actingon the rotor blade increase with increasing sweepback, an angle of 1 to45 degrees, preferably from 1 to 15 degrees, has proven to beadvantageous.

In addition, a fluid transition from the rotor blade into the end regionis advantageous as, in the case of an abrupt bend, additional pressurefluctuations occur in the region of the bend. They can result in areduction in power and additional noise.

Preferably in its end region the rotor blade according to the inventioninvolves a predetermined radius of curvature, wherein the curvatureparticularly preferably increases towards the rotor blade tip, that isto say the radius of curvature becomes less. By virtue of a suitablyselected curvature the end region of the rotor blade can be curvedmechanically at an angle of about 5 degrees while affording anaerodynamic effect which corresponds to an angle of 10 degrees. Thatembodies an advantageous acoustic result with at the same time alsoadvantageous aerodynamic characteristics.

At the same time however greater torsional moments occur in the rotorblade due to that sweepback configuration, and those torsional momentsalso act on the rotor blade connection. Naturally that also results in apermanently higher level of loading on the plant. In order to compensatefor that higher level of loading at any event for the rotor bladeconnection and the subsequent components of the wind power plant, it isparticularly advantageous for a central region of the rotor blade, thatis to say a region between the rotor blade root and the end region whichis swept back in the direction of the trailing edge, to be curved in thedirection of the blade leading edge. In that case that curve is of sucha dimension that the outer trailing edge of the swept back end region isno deeper than in the case of a blade without a swept back end region.

In that way torsional moments which act in opposite relationship occurin the rotor blade itself and with a suitable design cancel each otherout so that the rotor blade itself is admittedly still subjected to thatloading but the rotor blade connection and the further components of thewind power plant do not have to carry additional loads.

In order on the one hand to permit easy assembly and on the otherretro-fitment to already existing rotor blades, the end region ispreferably in the form of a portion which can be fitted into the rotorblade and preferably is of a length of not more than ⅓ of the rotorblade length and particularly preferably about 1/10 of the rotor bladelength.

In that case, in an advantageous development, that end region can behollow and at its end remote from the wake flow can have an opening forwater drainage so that fluid which collects in the rotor blade and whichis formed for example as a consequence of condensation effects and istransported by centrifugal force to the rotor blade tip can issue fromthe end region and thus be removed from the rotor blade.

In order to promote the effect of the end region according to theinvention, in accordance with the invention there is provided a rotorblade tip for a rotor blade having such an end region, wherein the rotorblade tip is in the form of an independent portion which can be fittedinto the end region of the rotor blade.

Alternatively, to obtain the object of the invention, a furtherdevelopment of a rotor blade tip of the kind set forth in the openingpart of this specification can be such that the ‘outer region’ narrows.That configuration for the rotor blade tip is based on the realizationthat the decreasing blade depth affords a reduced flow around the rotorblade tip as the energy thereof is previously distributed to thetrailing edge vortices but at the same time the effective rotor bladearea is reduced. The angled configuration of the rotor blade tip meansthat the effective rotor blade depth remains at its optimum to theangled rotor blade tip. The region which goes to a point extends at apredetermined preferred angle away from the plane of the rotor blade inthe direction of the pressure side of the rotor blade. In thatarrangement the vortex at the rotor blade tip is simultaneously detachedfrom the rotor blade plane and moved into another plane. That in turnhas a favorable effect on sound emission of the rotor blade equippedwith such a tip and at the same time reduces losses which occur at therotor blade. That involves both the edge vortex losses and the degree ofaerodynamic efficiency which can be improved by a suitable design, aswell as an advantageous configuration in respect of the pressure dropbetween the pressure and the suction sides.

In a particularly preferred feature the outer region of the rotor bladetip is curved out of the horizontal at an angle of about 70° to 90° outof the horizontal. In other words, the rotor blade tip includes an angleof about 110° to 90° with the rotor blade. In empirical investigations,the best results have been found with those angles.

In a particularly preferred development the rotor blade tip according tothe invention is in the form of an independent portion which can befitted into the rotor blade. In addition the rotor blade tip is hollowand preferably comprises metal, in particular aluminium. The hollowstructure affords a reduction in weight and thus greater ease ofhandling.

In addition a hollow rotor blade tip, like also a hollow end region of arotor blade as described hereinbefore, can have warm air flowingtherethrough, for example for eliminating or reducing icing.

In addition a rotor blade tip made from metal can serve as a lightningconductor and thus transfer lightning strikes into a suitable lightningarrester in order thereby to effectively protect the wind power plant inthe event of a lightning strike.

Advantageous developments of the invention are set forth in theappendant claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is described in greater detail hereinafter with referenceto the Figures in which:

FIG. 1 shows a plan view of a rotor blade according to the inventionwith a curved end region according to a first embodiment of theinvention,

FIG. 2 shows a rotor blade according to the invention with a curved endregion according to a second preferred embodiment of the invention,

FIG. 3 shows a further view of the second embodiment of the invention,

FIG. 4 shows still a further view of the second embodiment,

FIG. 5 shows a third embodiment of a swept back rotor blade,

FIG. 6 shows a side view of a rotor blade tip according to theinvention,

FIG. 7 shows a front view of an embodiment of a rotor blade tipaccording to the invention,

FIG. 8 shows a front view of an alternative embodiment of a rotor bladetip according to the invention,

FIG. 9 shows a front view of an alternative embodiment of a rotor bladetip according to the invention, and

FIG. 10 is a view of a rotor blade with the end region designed inaccordance with the invention and a rotor blade tip according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a rotor blade 10 having a leading edge 18 and a trailingedge 20 according to the invention of a wind power plant. The threadaxis 14 is indicated in the rotor blade 10. The thread axis 14 is anotional axis on to which all parts of a rotor blade are to be threadedso as to afford the desired rotor blade shape.

The end region 12 of the rotor blade 10 is bent at a predetermined angleα with respect to a first thread axis 14. A second thread axis 16 isillustrated for the end region 12, the angle α being specified betweenthe two axes 14, 16. In this Figure the angle α is 5 degrees. That valuerepresents an acceptable compromise between reduced sound emission andincreased loading.

Therefore the end region is bent in the rotor blade plane in thedirection of the rotor blade trailing edge 20. That bend results on theone hand in a longer trailing edge and thus a wider distribution of thevortex energy. On the other hand the flow breaks away at the trailingedge of the rotor blade 10 in the bent end region 12, later than in thestraight region of the rotor blade 10. As a result the noise-generatingvortices occur correspondingly later.

An improved embodiment of a rotor blade 10 according to the invention isshown in FIG. 2. This Figure also shows the thread axes 14, 16. It willbe noted however that the transition from the rotor blade 10 into theend region 12 does not occur here at a sharp bend but rather extendssteadily in the form of a curvature. It will be noted that the curvatureincreases towards the rotor blade tip. The radius of curvature thereforebecomes smaller towards the rotor blade tip.

In this case, in the end region 12 the arc tangent is displaced inparallel relationship at the tip of the rotor blade trailing edge 20 andtowards the center of the rotor blade. An angle β is defined between theaxes 14, 16. That angle is 10 degrees.

Those 10 degrees occur precisely out of the configuration of the arctangent at the rotor blade tip, in which respect however the providedsweepback of the rotor blade 10 is not greater than in the case of therotor blade 10 shown in FIG. 1. Accordingly the aerodynamiccharacteristics differ only slightly from the rotor blade shown in FIG.1 while however the acoustic characteristics are better by virtue of thegreater angle β.

That situation as set forth hereinbefore is described in greater detailwith reference to FIG. 3. In particular the end region 12 of the rotorblade 10 is shown in FIG. 3. The trailing edge of the end region 12 inthis case is shown bent on the one hand in a manner corresponding to theembodiment illustrated in FIG. 1. That variant is denoted by referencenumeral 21. At the same time the embodiment with the curved trailingedge 20 is also illustrated.

It can be clearly seen here that the outermost rotor blade tip at thetrailing edges 20 and 21 each occur at the same point; the rotor bladedepth is therefore unchanged from the aerodynamic point of view.

This Figure also shows the first thread axis 14 (original blade threadaxis). The arc tangent 17 which has been displaced in parallelrelationship and the second thread axis 16 (tip thread axis)corresponding to the trailing edge 21 of the end region are also shown.The angles α and β are also illustrated. The angle α is again 5 degrees.It is formed by the first thread axis 14 of the rotor blade 10 and thesecond thread axis 16 corresponding to the embodiment of the rotor bladeas shown in FIG. 1. The angle β is enclosed between the first threadaxis 14 and the arc tangent 17 corresponding to the embodiment shown inFIG. 2. The angle β is 10 degrees.

Here therefore it is particularly easy to see the advantage of theembodiment illustrated in FIG. 2.

FIG. 4 shows once again the swept back rotor blade 10 according to theinvention with the leading edge 18, the trailing edge 20 and the endregion 12 which is swept back in the direction of the trailing edge 20.Also shown in this Figure are two lines 22, 23 representing theconfiguration of the leading edge 18 and the trailing edge 20 withoutthe swept back end region 12. This Figure already clearly shows theextent to which the end region 12 is swept back by virtue of thesweepback in the direction of the trailing edge of the rotor blade 10.

FIG. 5 shows an alternative embodiment of the rotor blade 10 accordingto the invention which differs from the embodiment illustrated in FIG. 4by a central portion 13 which is swept in the direction of the leadingedge 18 of the rotor blade 10. It will be appreciated that the advantageof the fluid transition between the individual regions of the rotorblade 10 also applies in regard to that swept configuration. In thisrespect that sweep in the direction of the leading edge 18 is of such amagnitude that the outermost point of the end region 12 of the rotorblade, which is swept back in the direction of the trailing edge 20, isagain within the broken lines 22 which in this Figure also specify thenotional rectilinear configuration of the rotor blade.

That arrangement results in mutually oppositely acting torsional momentsin the end region 12 and the central region 13 of the rotor blade, whichcancel each other out when suitably dimensioned in terms of their actionat the rotor blade connection.

FIG. 6 shows a rotor blade 10 with an edge arc 30 according to theinvention, which extends away from the suction side 24 of the rotorblade 10, that is to say towards the pressure side of the rotor blade10. The upper edge 36 of the edge arc 30 is of a profile thickness whichis as small as possible in order to minimize as far as possible the edgevortices which are detached there, so that a level of sound emissionwhich is also as low as possible is involved.

The edge arc 30 is preferably bent out of the horizontal at an angle ofabout 60° to 90°. In other words, it includes an angle of between 120°and 90° with the rotor blade. That region is illustrated by two upwardlybent portions 30, 31 of which one is shown by a broken line.

FIG. 7 shows a front view of a first embodiment of the edge arc 30according to the invention. In this Figure the trailing edge 34 of theedge arc 30 and the upper edge 36 of the edge arc extend rectilinearlywhile the front edge 32 between the rotor blade leading edge 26 and theedge arc upper edge 36 extends away from the suction side 24 of therotor blade at a predetermined angle. That arrangement provides that theedge arc upper edge 36 is shortened in relation to the depth of therotor blade, as can be seen at the rotor blade suction side 24. Therotor blade therefore involves its aerodynamically fully effective depthas far as the edge arc 30 and it is only in the edge arc 30 that it goesinto a shorter edge arc upper edge 36.

At the same time the edge vortex which tears away at the rotor bladeupper edge 36 is guided out of the plane of the rotor blade 10 so thatthe edge vortex is guided away from the plane of the blade.

FIG. 8 shows an alternative embodiment of the edge arc shown in FIG. 7.While FIG. 7 shows an arc edge trailing edge 34 which extendssubstantially perpendicularly to the longitudinal axis of the rotorblade, that edge arc is also swept in the direction of the trailing edge34 in FIG. 8. That sweep configuration provides that the detachmentpoint 37 at which the flow becomes detached from that edge arc isdisplaced still further rearwardly and accordingly the energy of theedge vortices is still further distributed and the level of soundemission is still further reduced.

The operating principle is similar in the embodiment of the edge arc 30shown in FIG. 9. It will be noted that this edge arc 30 is optimized toafford an edge vortex which is as small as possible. For that purposethe edge arc leading edge 32 and the edge arc trailing edge 34 extendwith a predetermined curved and particularly preferably ellipticalgradient to the edge arc upper edge 36. In that case the edge arc upperedge 36 is again bent away from the rotor blade suction side 24, that isto say towards the pressure side, out of the plane of the rotor blade.

The elliptical configuration of the edge arc leading edge 32 and theedge arc trailing edge 34 at the same time increases the length of thedistance over which the flow separates from the rotor blade. That alsoresults in a reduced level of sound emission as a flow around the bladetip is very substantially eliminated, unlike the situation with bladegeometries which terminate in a blunt shape.

The ratio of depth to height (the depth is the width in the plan view inFIG. 9) of the angled portion of the arc edge is about 1:0.8 to 1.2,preferably 1:1. The ratio of the height of the angled portion of theedge arc to the depth of the rotor blade at the connection of the edgearc is about 1:1 to 1:1.3, preferably 1:1.14. In that respect the depthconfiguration in the angled portion of the edge arc is approximatelyhyperbolic (the profile width in a plan view) and the uppermost cappoint of the outermost profile section is at about 30 to 40%, preferably33% of the profile depth, with respect to the thread axis of the blade.

FIG. 10 shows a rotor blade 10 with a combination of a curved end region12 and an edge arc 30 adjoining same. In this case the curve of the edgeregion 12 from the leading edge 26 of the rotor blade to the trailingedge 20 and a curve of the edge arc 30 out of the plane of the rotorblade can be clearly seen. Accordingly the advantageous acoustic effectsof the curved end region 12 on the one hand and the angled edge arc 30on the other hand are combined here.

The described rotor blade according to the invention is part of a rotorof a wind power plant.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A rotor blade tip for a rotor blade with an aerodynamic profilehaving a pressure side and a suction side, wherein the rotor blade tipis curved in the tip region in the direction of the pressure side of therotor blade and having and edge arc extending from the tip end in thedirection of the pressure side, characterized in that in its tip regionthe rotor blade tip narrows towards an edge arc upper edge, and has anedge arc leading edge and an edge arc trailing edge; wherein the edgearc leading edge and the edge arc trailing edge extend equally in apredetermined, curved, gradient to the edge arc upper edge.
 2. The rotorblade according to claim 1 characterized in that the end region extendsat an angle of between 1 and 45 degrees relative to the thread axis. 3.The rotor blade according to claim 2 characterized in that the angle isin the region of 1 to 15 degrees.
 4. The rotor blade according to claim1 characterized in that the trailing edge of the rotor blade blendsfluidly into the trailing edge of the end region.
 5. The rotor bladeaccording to claim 4 characterized in that the trailing edge of the endregion is of a predetermined radius of curvature.
 6. The rotor bladeaccording to claim 5 characterized by an increasing curvature towardsthe rotor blade tip.
 7. The rotor blade according to claim 1,characterized in that the end region is in the form of an independentportion which can be fitted into the rotor blade.
 8. The rotor bladeaccording to claim 1 characterized in that the end region forms at most⅓ of the rotor blade length.
 9. The rotor blade according to claim 7characterized in that the end region has a region of reducedcross-section for fitting into the rotor blade.
 10. The rotor bladeaccording to claim 9 characterized in that at least one opening isprovided in the region of reduced cross-section.
 11. The rotor bladeaccording to claim 7 characterized in that the end region is hollow. 12.The rotor blade according to claim 11 characterized in that provided atits end remote from the afflux flow is an opening for water drainage.13. The rotor blade according to claim 12 characterized in that a tubeportion adjoins the opening.
 14. The rotor blade according to claim 1characterized by a region between the rotor blade root and the endregion, which region is angled in the direction of the leading edge. 15.The rotor blade according to claim 1 characterized in that the rotorblade comprises glass fiber-reinforced plastic material and thatconductive elements for lightning conduction are incorporated into therotor blade and are in conductive contact with the end region.
 16. Therotor blade tip for a rotor blade according to claim 1 characterized inthat the rotor blade tip is in the form of an independent portion whichcan be fitted into the end region of the rotor blade.
 17. A rotor bladetip for a rotor blade with an aerodynamic profile having a pressure sideand a suction side, wherein the rotor blade tip is curved or angled inits outer region in the direction of the pressure side of the rotorblade, characterized in that the outer region narrows.
 18. The rotorblade tip according to claim 17 characterized in that in the region ofthe curve the rotor blade profile blends fluidly into the profile of theouter region.
 19. The rotor blade tip according to claim 17characterized in that the cross-sectional plane of the outer regionextends at a predetermined angle relative to the cross-sectional planeof the rest of the rotor blades.
 20. The rotor blade tip according toclaim 17 characterized in that the rotor blade tip is in the form of anindependent portion which can be fitted into the rotor blade.
 21. Therotor blade tip according to claim 16 characterized in that the rotorblade tip has a region of reduced cross-section for fitting into therotor blade.
 22. The rotor blade tip according to claim 21 characterizedin that at least one opening is provided in the region of reducedcross-section.
 23. The rotor blade tip according to claim 16characterized in that the rotor blade tip is hollow.
 24. The rotor bladetip according to claim 23 characterized in that provided at its endremote from the afflux flow is an opening for water drainage.
 25. Therotor blade tip according to claim 24 characterized in that a tubeportion adjoins the opening.
 26. The rotor blade tip according to claim16 characterized in that it comprises metal, in particular aluminium.27. A rotor blade having a rotor blade tip according to claim
 17. 28. Arotor blade having a rotor blade tip according to claim 17,characterized in that the rotor blade comprises glass fiber-reinforcedplastic material and that conductive elements for lightning conductionare incorporated into the rotor blade and are in conductive contact withthe rotor blade tips.
 29. A wind power plant comprising a rotor providedwith at least one rotor blade according to claim 1.